I think we've reached a plateau of CPU performance. Clock speeds don't seem to be budging much anymore, just adding more cores, more cache and refining designs.

Really, I can't see much of a reason to upgrade any i5/i7 system out there right now, other than to show off. The only part that really needs upgrading frequently is the GPU I'd say.

And well we all know that there's no money to be had in the consumer market. All the profits come from server/enterprise gear so it's understandable that Intel would focus their efforts there. Also Sandy Bridge hasn't really penetrated the market much either, so Intel probably wants to ride that out and try to make some profit there too. That's why companies like IBM dropped out of the desktop business and only targeted the enterprise market.

I'd say the main issue is the lack of competition. Competition drives innovation. Without it, we get a stale, overpriced market. As such, AMD hasn't had the performance crown in ages, so Intel sees no reason to pour a ton of money into R&D of desktop parts.